The present invention relates to an oscillator with ohmically adjustable oscillation frequency.
Oscillators are circuits for generating high-frequency vibrations. The core of an oscillator is an active device having a non-linear characteristic curve, such as a transistor or a diode. The oscillation frequency f of the oscillator is determined by an oscillator circuit and its effective capacitance C and inductance L:
  f  =      1          2      ·      π      ·                        L          ·          C                    
The oscillator circuit, that can also be referred to as resonator, can be realized with all frequency-selective devices whose behavior can be described by an equivalent circuit diagram of capacitance and inductance. Examples of this are discrete LC oscillator circuits, dielectric resonators, cavity resonators or line resonators.
Apart from fixed-frequency oscillators having only one oscillation frequency, there are also oscillators that can be varied in their oscillation frequency. The oscillation frequency can be varied by mechanically or electrically changing frequency-determining devices of the oscillator circuit. Mechanically variable devices cannot be considered in many applications where fast frequency change is necessitated. For such applications, voltage-controlled devices are used in the oscillator. If voltage-controlled devices are used in oscillators, the same are called voltage-controlled oscillators or VCOs. In conventional VCO concepts, the voltage-dependent barrier layer capacitance of varactor diodes or the voltage-controlled capacitance of a transistor is used for changing the effective capacitance of the resonator and hence for varying the oscillation frequency of the oscillator.
A general problem of monolithically integrated circuits is the dependency on a certain technology and its transistor architecture. Thus, transistors are optimized for speed for the millimeter wave range, from which, however, no varactor diodes having optimum characteristics can be realized. Above that, monolithically integrated VCOs operating with varactor diodes frequently have a bandwidth of 5 to 8% in relation to the average oscillation frequency. A higher bandwidth of, for example, more than 10% with monolithically integrated varactor diodes is associated with increased effort and complexity.